In metallurgical vessels for electric-furnace steelmaking (e.g., DC arc furnaces) electrodes which are incorporated in the refractory lining of the vessel and which penetrate through this lining (bottom electrodes) serve as anodes for producing the electrical connection to the melt. Those parts of the electrode which are in contact with the molten metal are subject to high thermal wear. For this reason, various cooling devices for bottom electrodes have already been proposed.
By way of example, DE-A-38 35 785 proposes a cooling sleeve which surrounds and cools that part of the electrode which projects out from the vessel wall. The cooling power is low, since only a small region of the electrode is cooled, which region is situated far away from the thermally loaded contact surface between the electrode and the melt. For this reason, the electrode melts relatively quickly and its service life is low. Exchanging electrodes is complicated, since the new electrodes have to be embedded in the refractory material of the furnace wall.
It has therefore already been proposed (DE-B-40 26 897, DE-A-43 35 065) to provide cavities in the electrode body and to cool these cavities by spraying water. For safety reasons, these cavities are situated at a very considerable distance from that part of the electrode which is in contact with the molten metal, and are situated outside the furnace wall. This considerable distance is intended to ensure that in the event of the cooling failing, or in the event of an extraordinary thermal load on the electrode, the latter does not melt to a sufficient extent for molten metal to be able to break through into this cavity. Contact between the molten metal and cooling water can lead to explosive reactions, in particular if water is included in the molten metal, since the formation, eveporation, and expansion of steam tear explosively through the melt. Also, it is impossible to rule out the chemical decomposition of the water followed by detonating gas reactions. Moreover, molten metal breaking through into the cavities could mean that the furnace leaks via the burnt-through electrode and the cavities.
The large distance between cooled cavities and molten metal, which is selected for safety reasons, means that the cooling action is unsatisfactory and, consequently, also means a high electrode wear.
Furthermore, there is a need to cool wall regions of metallurgical vessels (e.g. electric arc furnaces) which are subject to particularly high thermal loads, so as to reduce the wear to the vessel wall. For the same reasons as those cited above, a water cooling system is problematical, as the abovementioned risk of explosion remains. If, under extraordinary operating conditions, molten metal breaks through the vessel wall into such a cooling element, under certain circumstances the vessel can leak via this region which has been burnt through.